Simplify the following expression: $q = \dfrac{9n}{8} - \dfrac{n}{5}$
Explanation: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $8$ and $5$ $\lcm(8, 5) = 40$ $ q = \dfrac{5}{5} \cdot \dfrac{9n}{8} - \dfrac{8}{8} \cdot \dfrac{n}{5} $ $q = \dfrac{45n}{40} - \dfrac{8n}{40}$ $q = \dfrac{45n -8n}{40}$ $q = \dfrac{37n}{40}$